Plate type heat exchanger

ABSTRACT

The heat exchanger of the plate-fin type comprises at least three plates, the adjacent surfaces of which have spaced rows of extended surface elements. Each of the extended surface elements are curved in a direction away from its associated plate surface. The rows of extended surface elements of the adjacent surfaces are alternately arranged and with the extended surface elements of one plate surface positioned with its curvature in juxtaposed and opposite position relative to the curvature of extended surface elements of the next adjacent row of extended surface elements. The length, spacing and curvature of the extended surface elements are correlated so that when the heat exchanger is in use, the distal end of a first extended surface element abuts the next adjacent second surface element of the opposite plate surface in the area of the point of attachment of the latter to the opposite plate and the first surface element abuts at a point spaced from its distal end the next adjacent third surface element projecting from the opposite plate at a substantially corresponding point spaced from the distal end of the said third surface element. This interlocking and abutting relationship of the extended surface elements of opposite plates provides an assembly of high structural strength for resisting the flexure of the plates toward each other under a high differential pressure across the plates.

United States Patent 1 Haberski June 26, 1973 PLATE TYPE HEAT EXCHANGER [75] Inventor: Richard Joseph Haberski, Emerson,

[73] Assignee: Curtiss-Wright Corporation,

Wood-Ridge, NJ.

22 Filed: Nov. 1, 1971 21 Appl. No.: 194,136

France 165/170 Primary Examiner-Charles J. Myhre Assistant Examiner-'Theophil W. Streule, Jr. Attorney-Arthur Frederick et al.

[57] ABSTRACT The heat exchanger of the plate-fin type comprises at least three plates, the adjacent surfaces of which have spaced rows of extended surface elements. Each of the extended surface elements are curved in a direction away from its associated plate surface. The rows of extended surface elements of the adjacent surfaces are alternately arranged and with the extended surface elements of one plate surface positioned with its curvature in juxtaposed and opposite position relative to the curvature of extended surface elements of the next adjacent row of extended surface elements. The length, spacing and curvature of the extended surface elements are correlated so that when the heat exchanger is in use, the distal end of a first extended surface element abuts the next adjacent second surface element of the opposite plate surface in the area of the point of attachment of the latter to the opposite plate and the first surface element abuts at a point spaced from its distal end the next adjacent third surface element projecting from the opposite plate at a substantially corresponding point spaced from the distal end of the said third surface element. This interlocking and abutting relationship of the extended surface elements of opposite plates provides an assembly of high structural strength for resisting the flexure of the plates toward each other under a high differential pressure across the plates.

9 Claims, 4 Drawing Figures PLATE TYPE HEAT EXCHANGER DISCLOSURE This invention relates to heat exchangers and, more particularly, to plate-type heat exchangers having extended surface elements.

BACKGROUND OF THE INVENTION The heat exchange efficiency of plate fin type heat exchangers, employing extended surface elements or secondary elements, is largely dependent upon the rate of heat conductivity betwen the secondary elements and the primary plates which define the fluid conduits. Where the secondary elements are internally metallically bonded to the primary plates, as by welding, brazing or the like, it is important that the metallic bonds provide a substantially uninterrupted contact between the secondary element and the primary plates in order to provide a high heat conductive path across the joint between the primary plates and the secondary elements. A high coefficient of heat transfer, as herein discussed, is of particular importance in heat exchangers wherein indirect heat transfer is to be effected between gaseous fluids.

Other important considerations in the design of a heat exchanger of the plate fin type are the matters of structural strength and a fluid tight seal between the fluid flow paths. In coventional heat exchangers of the plate fin type, structural strength is dependent upon the convoluted secondary elements and fluid scaling is dependent upon the continuity and integrity of the metallic bond between secondary elements and the primary plates. High structural strength is particularly important in heat exchange apparatuses where there is a high pressure differential betwen the fluids which are passed in heat exchange relationship with each other. To increase the coefficient of heat transfer, some conventional heat exchangers of the type herein discussed, are provided with baffling or turbulators disposed -in the fluid flow paths. Typical exchange apparatuses wherein both high coefficient of heat transfer and structural strength are essential is in aftercoolers for supercharged aircraft engines, as exemplifred in the U. S. Pat. to Ackerman et al., No. 2,646,027, and in exhaust gas economizers for gas turbine engines, such as disclosed in the U. S. Pat. to Staley, No. 2,609,664.

Accordingly, an object of the present invention is to provide a heat exchanger of the plate fin type which has both a high coefficient of heat transfer and structural strength without reliance upon the integrity of a metallic bond between the secondary elements and the primary plates.

Another object of this invention is to provide a heat exchanger of the plate fin type which does not require turbulators for achieving a high coefficient of heat transfer.

A further object of this invention is to provide a heat exchanger of the plate fin type which is relatively inexpensive and easy to fabricate.

A still further object of the present invention is to provide a heat exchanger of the plate fin type which is not dependent upon internal metallic bonding of secondary elements to the primary plates for structural strength.

SUMMARY OF THE INVENTION The present invention, therefore, contemplates a heat exchanger comprising a plurality of spaced plates to form adjacent fluid flow passageways for fluids between which heat transfer is to be effected. Inlet and outlet header means are provided for each of the fluid streams, which inlet and outlet header means are disposed in communication with opposite ends of the fluid flow passageways and sources of fluid and places of use or storage of fluid so that flow of fluids through the passageways is achieved. The adjacent surfaces of the plates defining each of the fluid flow passageways (hereinafter referred to as the primary plate surface) is provided with a plurality of spaced rows of extended surface elements (hereinafter referred to as secondary surface elements), the rows extending in alignment with the direction of fluid flow through the passageway. Each of the secondary surface elements are curved in a direction away from its associated primary plate surface. The rows of secondary surface elements of one primary plate surface are arranged to extend in alternate relationship with the rows of secondary surface elements of the opposite primary plate surface and with the curvature of the secondary surface elements of one primary plate surface disposed to extend in an opposite direction to the curvature of the secondary surface elements of the opposite primary plate surface. The length of the secondary surface elements, spacing between rows of secondary surface elements and the degree of curvature of the secondary surface elements are correlated so that when the heat exchanger is in use, substantially all the secondary surface elements are in abutment at two spaced points. One of the points of abutment is the distal end of a first surface element engaging the next adjacent second surface element projecting from the opposite plate surface at the point of attachment of the latter to its associated plate surface, the other point of abutment of the first surface element being a point on its convex surface which engages a substantially corresponding point on a next adjacent third surface element projecting from the opposite plate. This interlocking relationship of secondary surface elements of the opposite primary plate surfaces provides the assembly with structural strength to resist flexure of the plates toward each other under compressive loading.

It is preferred that the extended surface elements be formed by a skiving process, such as revealed in the U. S. Pats. to Kritzer, No. 3,202,312 and No. 3,229,722. This method of forming the extended surface elements avoids the time consuming and relatively expensive step of metallically bonding such elements to the primary plate surface. It also insures optimum heat conductivity between the extended surface elements and the plate.

- It is also preferred for optimum coefficient of heat transfer to provide spaces between each of the ex tended surface elements in each row to induce turbulence in the fluid flows and thereby increase surface conductance betwen the fluid and the surface elements and plate surfaces. This can be achieved by tapering the ribs outwardly from theprimary plate surface or by spacing the ribs from each other along the primary plate surface.

BRIEF DESCRIPTION OF DRAWINGS The invention will be more fully understood from the following description when considered in connection with the accompanying drawings in which:

FIG. 1 is a schematic cross-sectional view of a gas turbine engine having attached thereto an exhaust gas economizer constructed in accordance with the present invention and diagrammatically shown therein;

FIG. 2 is a cross-sectional view taken along line 2-2 of FIG. I on an enlarged scale; 1

FIG. 3 is a view in cross-section taken along line 3-3 f FIG. 2; and

FIG. 4 is a fragmentary, enlarged view in crosssection of one of the fluid flow paths of the heat exchanger of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Now referring to the drawings and, more specifically, to FIG. I, the reference number generally identifies the heat exchanger according to the present invention, which for purposes of this disclosure is shown as an exhaust gas economizer for a gas turbine engine 12. While heat exchanger 10 of this invention is shown in association with a gas turbine engine, it is to be understood that the invention is not limited to such application, but may be employed wherever indirect heat exchanger is to be obtained between a plurality of fluids without departure from the scope and spirit of the invention. Although heat exchanger 10 is not limited in application to a gas turbine engine, it is particularly suited for such use because it has the structural strength to accommodate the high differential pressure 'between the compressed air and the exhaust gases,

which differential pressure can range between about 40 and about 225 pounds per square inch.

The typical gas turbine engine for industrial purposes comprises essentially a casing 11 having an inlet section (not shown) which communicates with a source of air and with a compressor section 14 to deliver air to the latter. An annular compressed air mainfold 16 is provided to receive compressed air from the compressor section 14. A plurality of circumferentially spaced compressed air conduits 18 extending externally of casing 11 are connected at one end to manifold 16 and at the opposite end to an annular air inlet mainfold 20 of heat exchanger 10. The compressed air after passing in indirect heat exchange relationship with exhaust gases in heat exchanger 10 flows, via a plurality of external outlet conduits 22 (only one being shown in the drawings), to a fuel combustor 24. The doughnut shaped combustor 24 has a plurality of circumferentially spaced fuel vaporizer tubes 26 which are connected to receive fuel from a suitable source thereof (not shown). The fuel is mixed in the combustion chamber 28 with the compressed air delivered to the chamber through perforations in the combustor walls. After combustion of the fuel in chamber 28, the gaseous products of combustion are expanded through a turbine 30. From the turbine the exhaust gases are discharged into heat exchanger 10 through a discharge port 32 in the end wall of casing 11. The exhaust gases which are at relatively low pressure and high temperatures are then passed in indirect heat exchange with the compressed air passing through heat exchanger 10. The relatively cool exhaust gases are discharged from heat exchanger 10 to atmosphere or to device (not shown) where further heat might be extracted from the exhaust gases. The turbine is provided with vaned rotors 34 which are connected to a primary power take-off shaft 36 and a compressor drive shaft 38, the power take-off shaft 36 being connected to drive a device, such as an electric generator (not shown), while shaft 38 drives the vaned rotors 40 of compressor section 14.

The heat exchanger 10 comprises a housing or casing 42 0f generallydoughnut configuration and having an inner wall 44 which is connected to the end wall of the gas turbine casing 11 adjacent discharge port 32. An exhaust gas inlet port 46, complementary to discharge port 32, is provided in inner wall 44 to permit entry of exhaust gases into the heat exchanger. The casing 42 has a conical shaped central portion extending axially and inwardly toward the gas inlet port 46. Within casing 42 is supported circumferentially spaced compressed air ducts 50, the space between air ducts 50 defining exhaust gas passageways 52. The air ducts and exhaust gas passageways are so disposed within casing 42 to divide the interior of casing 42 into an annular exhaust gas inlet header or chamber 54 and an annular exhaust gas outlet header or chamber 56. One or more exhaust gas discharge connections 58 are provided in outer wall 48 of casing 42 to receive and conduct exhaust from the heat exchanger. The conical shaped central portion of easing wall 48 serves to define the annular exhaust gas inlet header 54 and to deflect the entering axial flow of exhaust gas, through gas inlet port 46, into exhaust gas inlet header 54 and radially, outwardly toward exhaust gas passageways 52.

As best shown in FIG. 2, each air duct 50 is constructed of two spaced primary plates 60 and 62 and inner and outer plates 64 and 66 connecting the opposite adjacent end portions of plates 60 and 62. The plates 60, 62, 64 and 66 are dimensioned to extend between inner wall 44 and outer wall 48 (see FIG. 1) and are attached by welding or in some other suitable fluid tight manner well known to those skilled in the art. Each of the ducts 50 is in communication with air inlet manifold 20 to receive compressed air and with an air outlet mainfold 70 which is connected to inner casing wall 44 in concentric, spaced relation to air inlet mani fold 20. The air outlet manifold 70 is in communication with ducts 50 to receive heated compressed air from the latter. The heated air is then passed from the outlet manifold 70 to outlet conduits 22 for delivery to combustor 24. To promote the transfer of heat between the exhaust gas flowing through passageways 52 and com pressed air in ducts 50, primary plates 60, 62 are provided with extended surface elements or secondary surface elements in accordance with the present invention.

As best illustrated in FIGS. 3, the opposite, juxtaposed surfaces of primary plates 60 and 62 are provided with spaced, parallel rows of secondary surface elements 72 and 74, respectively. Preferably, second ary surface elements 72 and 74 are produced by the skiving process as disclosed in the U. S. Pats. to Kritzer No. 3,202,312 and No. 3,229,722, so that optimum heat conductivity is assured between the secondary elements and their associated primary plates. Each of the secondary elements 72 and 74 are relatively thin and curved upwardly and toward an imaginary plane containing its connection with its associated primary plate or the root 76 (see FIG. 3). The rows of secondary elements 72 and 74 are arranged in alternate juxtaposition to each other so that the curvature or bend of the secondary elements 72 extend opposite to the curvature of secondary elements 74. The degree of curvature of secondary elements 72 and 74 is determined in relation to the spacing between primary plates 60 and 62 and the spacing between the rows of secondary elements so that, in assembly, the rows of secondary elements 72 of primary plate 60 can be readily brought into alternate, juxtaposition relationship with the rows of secondary elements 74 of primary plate 62 by merely moving primary plates 60 and 62 toward each other. Also, the degree of curvature relative to the spacing of the primary plates and the rows of secondary elements is such that each secondary element 72, 74 of opposite primary plates 60, 62 abut another secondary element of the opposite primary plate at a point spaced from its root 76 and at its distal end against the said other secondary element in the root-area of the latter element.

The aforesaid points of abutment between the rows of secondary elements 72 and 74 function to absorb the compressive forces tending to bend primary plates inwardly toward each other. As indicated by the arrows, C, each of the secondary elements function to convert the compressive forces acting against plates 60 and 62 into force components directed parallel to the primary plate as indicated by the arrows, B. These forces are absorbed or dissipated by equal and opposite force components B exerted by the abutting secondary elements. Thus, the primary plate assembly of heat exchanger has the structural strength to accommodate substantial pressure differential across the plates. This high structural resistance to compressive forcespermits the primary plates to be of relatively thin construction and thereby improve the coefficient of heat transfer by bringing the two fluids between which heat transfer is to occur into as close a direct surface-to-surface contact as is possible. In addition, the thin construction of the primary plates and secondary elements minimizes gaseous pressure losses which further contributes to the high efficiency of the heat exchanger.

While the abutment of juxtaposed rows of secondary elements 72 and 74 is essential to provide the heat exchanger with the desired structural strength and rigidity, such abutment is not essential when heat exchanger 10 is not under load. If secondary elements 72 and 74 are out of contact at their distal ends or at the points between the distal ends and their root areas 76, such non-abutment is not objectionable, providing under load and before appreciable flexure of primary plates 60 and 62 the secondary elements 72 and 74 come into abutment as herein described. Also, while the distal ends of secondary elements 72 and 74 are preferably in engagement in the area of the root portion of the secondary element of the oppositely disposed plate when under load, the distal ends may abut the surface of the opposite plate without departure from the scope and spirit of this invention.

The rows of secondary elements 72 and 74 are disposed in alignment with the direction of compressed air and exhaust gas flow so that the fluids pass between the rows and on both sides of secondary elements 72 and 74. To improve and promote the transfer of heat and minimize the formation of a fluid boundary layer adjacent the surfaces of the secondary elements and plate surfaces, secondary elements 72 and 74 may be provided, as shown in FIG. 2, with spaced notches 78. These notches 78 may be formed, by providing the ribs (not shown), from which the secondary elements may be formed by skiving, with tapered side walls or the ribs may be disposed in close spaced relationship to each other. Also, as is well known in the art of skiving, the

curvature of secondary elements 72 and 74 is achieved by a deflecting plate disposed adjacent the cutter blade and movable with the latter to impart to the material a predetermined curvature as the secondary element is being cut.

The heat exchanger 10, according to this invention, coacts with gas turbine engine 12 to effect heat transfer between compressed air and exhaust gases in the manner hereinafter described. Compressed air entering the gas turbine engine through an inlet (not shown) is conducted to compressor section 14 where the air is compressed. The compressed air passes from compressor section 14 into air manifold 16 and, thence, through the plurality of conduits 18, into air inlet manifold 20 of heat exchanger. From inlet manifold 20, the compressed air flows into the peripherally arranged air ducts and in indirect heat exchanger relationship with hot exhaust gas flow through passageways 52 which are located between and defined by air ducts 50. The relatively cool, high pressure compressed air, in passing in heat transfer relation to the high temperature exhaust gases, is heated while the exhaust gases are cooled; thus effecting the conservation of heat by putting back into the apparatus heat which would otherwise be lost. The cooled exhaust gases pass from passageways 52 into exhaust gas outlet chamber 56 and thence, from the apparatus through one or more discharge connections 58. The heated compressed air flows from ducts 50 into annular outlet manifold 70 and thence, through the plurality of outlet conduits 22, to combustor 24. The heated compressed air enters the combustor through the perforations in the combustor walls to support combustion of fuel which is delivered to the combustor by fuel lines, not shown. The gaseous products of combustion pass from combustor 24 into the turbine 30, where the exhaust gas is expanded through vaned rotor 34 to rotatively drive shafts 36 and 38. The expanded, high temperature exhaust gases pass from the turbine into and through discharge port 32 and inletport 46 of heat exchanger 10. From inlet port 46, the exhaust gases flow into inlet chamber 54 and, from the latter, through passageways 52. In flowing through passageways 52 the exhaust gases pass in indirect heat exchanger relationship to compressed air flowing through ducts 50 as previously described herein.

Although heat exchanger 10, as herein shown and described, provides counter-current flow of fluids, the invention is not to be limited to such construction. The primary plates and 62 may be provided with rows of secondary surface elements 72 and 74 which are arranged to provide cross flow of fluids relative to each other without departure from the scope and spirit of this invention. More specifically, each of the primary plates may be provided with rows of secondary elements on one side extending in non-parallel relationship to the rows of secondary surface elements on the opposite side of the same primary plate.

It is believed now readily apparent that the present invention provides a heat exchanger of the plate-fin type which is of relatively simple and inexpensive construction. It is a heat exchanger which provides a high coefficient of heat transfer as well as high structural strength to affect heat transfer between fluids having a great pressure differential.

Although but one embodiment of the invention has been illustrated and described in detail, it is to be expressly understood that the invention is not limited thereto. Various changes can be made in the arrangement of parts without departing from the spirit and scope of the invention as the same will now be understood by those skilled in the art.

What is claimed is:

l. A heat exchanger of the plate fin type for effecting indirect heat transfer between a plurality of fluids at different temperatures, comprising:

a. a pluralityof spaced plates to define therebetween a plurality of fluid passageways;

b. means for providing flow of fluids through said passageways so that the fluids pass in indirect heat exchanger relationship with each other;

c. each of said plates having spaced rows of extended surface elements projecting from the opposite sur faces defining each of said passageways;

d. each extended surface element has a curvature ex-- tending in a direction away from its associated plate surface; e. the rows of surface elements of opposite plate surfaces being disposed in alternate relationship to so that substantially all of the extended surface ele-- ments of one plate surface are in abutment against the extended surface elements of the opposite plate surface at their curved portions and at their distal end portions are in'abutment against the opposite plate surface in the area of attachmentof the surface elements'associated with the opposite plate surface whereby the extended surface elements coact to dissipate forces tending to compress'the plates together by converting the forces into force components directed counter to each other.

2. The apparatus of claim 1 wherein there are at least three plates defining therebetween two fluid passageways.

3. The apparatus of claim 1 wherein said extended surface elements are formed from the surface of their associated plates by skiving.

4. The apparatus of claim 1 wherein said plates are arranged in circumferential spaced relationship with each other. 7

5. The apparatus of claim 1 wherein said extended surface elements in each row are in close spaced relationship to each other.

6. The apparatus of claim 1 wherein said rows of extended surface elements extend in alignemnt with the direction of flow of the fluids through said fluid passageways.

7. A heat exchanger of the plate fin type for effecting indirect heat transfer between a plurality of fluids at different temperatures, comprising: 7

l a. a plurality of spaced plates to define therebetween a plurality of fluid passageways; I 1

b. means for effecting flow of fluids through said passageways so that the fluids pass in indirect heat exchange relationship with each other;

c. eachof said plates having spaced rows of extended surface elements projecting from the opposite surfaces defining each of said passageways; I

d. each extended surface element has a curvature extending in a direction away from its associated plate surface and back toward an imaginary plane containing the point of attachment of the extended surface elementto its associated plate;

e. the rows of surface elements extending from one plate surface being disposed between the rowsof surface elements extending from the opposite plate surface and with the curvature of the surface elements in one row of said one plate surface lying in a direction opposite the curvature of the surface elements in the next adjacent row projecting from the opposite plate surface;

f. the extended surface elements being dimensionedso that the distal endof a first surface element engages the next adjacent second surface element of the opposite plate surface in the area of the point of attachment of the latter to the opposite plate and the first surface element also abuts at a point spaced from its distal end the next adjacent third surface element projecting from the opposite plate surface at a substantially corresponding point surface elements are formed from their associated surfaces by skiving. V 

1. A heat exchanger of the plate fin type for effecting indirect heat transfer between a plurality of fluids at different temperatures, comprising: a. a plurality of spaced plates to define therebetween a plurality of fluid passageways; b. means for providing flow of fluids through said passageways so that the fluids pass in indirect heat exchanger relationship with each other; c. each of said plates having spaced rows of extended surface elements projecting from the opposite surfaces defining each of said passageways; d. each extended surface element has a curvature extending in a direction away from its associated plate surface; e. the rows of surface elements of opposite plate surfaces being disposed in alternate relationship to each other with the curvature of the surface elements in one row of said one plate surface lying in a direction opposite the curvature of the surface elements in the next adjacent row of the opposite plate surface; f. the extended surface elements being dimensioned so that substantially all of the extended surface elements of one plate surface are in abutment against the extended surface elements of the opposite plate surface at their curved portions and at their distal end portions are in abutment against the oppoSite plate surface in the area of attachment of the surface elements associated with the opposite plate surface whereby the extended surface elements coact to dissipate forces tending to compress the plates together by converting the forces into force components directed counter to each other.
 2. The apparatus of claim 1 wherein there are at least three plates defining therebetween two fluid passageways.
 3. The apparatus of claim 1 wherein said extended surface elements are formed from the surface of their associated plates by skiving.
 4. The apparatus of claim 1 wherein said plates are arranged in circumferential spaced relationship with each other.
 5. The apparatus of claim 1 wherein said extended surface elements in each row are in close spaced relationship to each other.
 6. The apparatus of claim 1 wherein said rows of extended surface elements extend in alignemnt with the direction of flow of the fluids through said fluid passageways.
 7. A heat exchanger of the plate fin type for effecting indirect heat transfer between a plurality of fluids at different temperatures, comprising: a. a plurality of spaced plates to define therebetween a plurality of fluid passageways; b. means for effecting flow of fluids through said passageways so that the fluids pass in indirect heat exchange relationship with each other; c. each of said plates having spaced rows of extended surface elements projecting from the opposite surfaces defining each of said passageways; d. each extended surface element has a curvature extending in a direction away from its associated plate surface and back toward an imaginary plane containing the point of attachment of the extended surface element to its associated plate; e. the rows of surface elements extending from one plate surface being disposed between the rows of surface elements extending from the opposite plate surface and with the curvature of the surface elements in one row of said one plate surface lying in a direction opposite the curvature of the surface elements in the next adjacent row projecting from the opposite plate surface; f. the extended surface elements being dimensioned so that the distal end of a first surface element engages the next adjacent second surface element of the opposite plate surface in the area of the point of attachment of the latter to the opposite plate and the first surface element also abuts at a point spaced from its distal end the next adjacent third surface element projecting from the opposite plate surface at a substantially corresponding point spaced from its distal end.
 8. The apparatus of claim 7 wherein the extended surface elements are each relatively small in cross-sectional dimension as compared with the cross-sectional dimension of the plates.
 9. The apparatus of claim 7 wherein the extended surface elements are formed from their associated surfaces by skiving. 